Design of Efficient XTEA Using Verilog

International Journal of Scientific and Research Publications, Volume 2, Issue 6, June 2012 1 ISSN 2250-3153

Shweta Gaba, Iti Aggarwal, Dr. Sujata Pandey

Electronics and Communication Engineering, Amity School of Engineering and Technology, Amity University, India

Abstract- In this age of viruses and hackers of electronic units but we are developing in a single module. The unit accepts eavesdropping and electronic fraud, security is paramount. A data in data_in1 and data_in2, a key in key, a delta in delta and cryptographic system ( or a cipher system) is a method of hiding the mode in block („00‟ for encipher, „11‟ for decipher). The data so that only certain people can view it. A cryptographic all_done wire is raised when the results of the operation are system typically consists of algorithms, keys, and key ready to be read from out_1 and out_2. It needs to be reset before management facilities. There are several algorithms to choose each use. The paper is arranged as follows: from that vary in the security they provide, their size, the time it takes to encrypt or decrypt a block of data. In this paper, we 1) Abstract analyze and evaluate the development of a cheap and relatively 2) Introduction fast hardware implementation of the extended tiny encryption 3) Verilog designing of XTEA algorithm (XTEA). Originally the research was split into separate 4) Results of simulation and synthesis encipher/decipher units, but these have now been combined into 5) Conclusions a single unit. The design will start by using finite state machine (FSMs) and will use Verilog hardware description language to describe the design. Minimizing the chip area and security transmission of data will be our main goal. The targeted II. IDENTIFY, RESEARCH AND COLLECT IDEA hardware systems are the reconfigurable Spartan III and Xilinx After attending the conference on VLSI MEMS and NEMS Virtex IV modern field programmable gate arrays (FPGAs). held in Amity University we got an idea to do some research work on XTEA. We have studied some research papers and Index Terms- Encipher, Decipher, Finite State Machines, Google it thoroughly. Till now a key of different 128 bit is cryptographic system. required for both encipher and decipher but we have design it in such a way that we require same key for both encipher an I. INTRODUCTION decipher module. he security of symmetric cryptosystem [9] is a function of T two parameters: the strength of the algorithm and the length III. EXPERIMENTAL DETAILS of the key. The algorithm must be so secure that there is no better XTEA [1] is a symmetric block cipher designed to correct way to break it than with a brute-force attack. The security of the weakness in TEA [6]. Like TEA, XTEA is a 64-bit block Feistel algorithm must be resided in the key and delta value we choose. network with a 128-bit key and a suggested 64 rounds. Several So therefore, there is balance between choosing long key, delta differences from TEA are apparent, including a somewhat more and the time required to complete the enciphering operation. complex key-schedule and a rearrangement of the shifts, XORs Many encryption algorithms [8] are available in the market and and additions (Hong et al. 2003; Ko et al.2004). Fig.1 shows the the selection of a specific one is dependent on the relatively tight block diagram of an XTEA. constraints. The selected algorithm should be small, relatively secure, with a proven history of overcoming possible well known attacks on it. The Tiny Encryption Algorithm (TEA) (Wheeler and Needham 1994), [6] and hence its successor the Extended- TEAs (XTEAs) (Needham and Wheeler 1997; Russell 2004; Kelsey et al. 1997; Moon et al. 2002) [7] are among the best choices available for security purpose. The name of block cipher came from the fact that block cipher encrypts plaintext as blocks [8]. These blocks differ in size between block cipher algorithms, for example, in Data Encryption Standard DES the plaintext is divided into blocks of length 64, but it is 32 in International Data Encryption Algorithm (IDEA) [11], if the length of block cipher equal one them, it will become stream cipher.

This paper uses the Verilog description language to implement the core function of XTEA and integrate them into a FPGA [10] chip. XTEA consist of two parts namely encipher and decipher

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The two main components of the XTEA such as the encipher and decipher are described below: A. Encipher Module To use the encipher.v, the inputs are two 32-bit U32 data values, the number of iterations and the 128-bit key value. The key is represented as a four 32-bit hexadecimal values. Key values can be created using a 128-bit key generator. The output from the system is two 32-bit values that are the encrypted version of the input. The Feistel function is used for encrypting the data and which is shown below in Fig.3.

Fig.1 Block Diagram of XTEA

In this proposed XTEA we are using different value of DELTA and KEY to increase the security. By doing this only the sender and receiver knows the value of both delta and key. And we also use 32 cycles for encrypting and decrypting the data in Feistel function to increase the security. Fig.2 shows the block diagram of a single XTEA round.

F Fig.3 Flow diagram for data encryption using Feistel function

B. Decipher Module To use the decipher.v the inputs are two 32-bit U32 data values, the number of iterations, and the 128-bit key value. The key is represented as four 32-bit hexadecimal values. The input data should be the encrypted data from the encipher.v and having the same 128-bit key value which is used in the encryption process. In this module an additional delta value i.e. also called magical value is included in the project and is used to implement the logic of the algorithms but in this programming we can use any hexadecimal value of 32-bit.The Feistel function is used to decrypt the data and shown below in Fig.4:

Fig.2 A single XTEA round with its normal computational constructs. The crossed square for the sum, crossed circle for an XOR, >> for a right shift, << for a left shift.

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data. So, we use Mealy Machine because mealy Machines use less number of states than Moore machine. In this state diagram, after resetting all the data at S0 state decides whether data has to be encrypted or decrypted. This is done by Block: If “Block=00” data goes for encryption i.e. state S1 and If “Block=11” data goes for decryption i.e. State S9. After engaging the Encrypt signal, the system will enter the state s1, and will finish the encryption after busy signal goes low (x>32) and we get data at state S7. In the same manner, data which will be decrypted goes for decryption i.e. state S9.After engaging the Decrypt signal ,the system will enter the state S9,and will finish the decryption after busy signal goes low(x>32) and will get the decrypted data at S7. It must be noted that the encrypted data must be sent as input for decryption to get the same input data (as in encryption process) as output.

V. RESULTS AND DISCUSSIONS The proposed XTEA has been simulated on the ModelSim SE 10.0a and has been synthesized on the Xilinx ISE 10.1. The Fig.4 Flow diagram for data decryption using Fiestel function figure 1 shows the generalized block diagram of XTEA with the maximum frequency of 129.099 MHz in case of Virtex4 and 71.114MHz in case of Spartan3. IV. STATE DIAGRAM OF XTEA In Fig.6, we show the waveforms of testing the encryption The state diagram of XTEA shows that how our XTEA works process. The reset signal was activated at first to insure that all and tells about the actual flow of data during encryption and the registers are cleared before starting any operation, note that decryption and shown below in Fig.5: the asynchronous reset is active high once. After that low the reset and select the block to set the module. Now, the module is ready to either encrypt or decrypt. One can distinguish between these two by the control signal i.e. block provided as an input to the system. After engaging the Encrypt signal, the system will enter the state s1, and will finish the encryption after busy signal goes Low (x>32). You can notice that the output is available at that time when x is equal to 32 which can easily shown in Fig.7.

Fig.5 State diagram of XTEA

While coding for XTEA, we want our algorithm which utilize Fig.6 Testing the Encryption Process (shows the starting Portion of the minimum chip area and provide more security transmission of waveform).

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FIG.7 Testing the Encryption Process (shows the Output after x is equal to 32) FIG.9 Testing the Decryption Process (shows the Output after x is equal to 32).

In Figure 8, we depict the waveforms of decryption state transition testing. The encryption and the Decryption processes VI. RTL SCHEMATIC are quite the same in architecture, but the decryption operates in The top module of the XTEA is shown below which we will get a reverse manner on the data, and uses a subtract or rather than after synthesize our main module on Xilinx ISE 10.1. an adder. This test shows the transition of the state from the S0 to S9, because block is selected for decryption and here the input given is same as of output of encryption module, and will finish the decryption after busy signal goes high. You can notice that the output is available at that time when x is equal to 32 which can easily shown in figure 9.

Fig.10 INTERNAL STRUCTURE OF XTEA WITH TWO BLOCKS - ENCIPHER AND DECIPHER

VII. SYNTHESIS RESULT The synthesis result contains a table which shows the comparison between the old research and the proposed XTEA. While doing comparison we will find that our research shows

Fig. 8 Testing the Decryption Process (shows the starting Portion of the great significance as our all the parameters are consuming less waveform). area and consumes less power to operate.

TABLE.1Comparison between old research and proposed XTEA

Parameters Virtex4SX25 Virtex4SX25 Spartan3s200tq FF668 FF668 [3] 144-4 LUTs 1252 4,608 1182

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Clock [7] Wheeler, David J. and Needham, Roger M. TEA Extensions. Computer Period(ns) 7.746 6.403 14.062 Laboratory, Cambridge University, England. October, 1997. Slice flip [8] Scheier, Bruce.” A Self-Study Course in Block-Cipher Cryptanalysis”, Crypto logia, Vol.24 (1).January 2000. flops 244 1,081 259 [9] Feistel, Horst.” Cryptography and Computer Privacy”, Scientific American. Maximum 129.099MHz 156.177MHz 71.114MHz Vol. 228(5). May 1973. frequency [10] Ke Wang,” An Encrypt and Decrypt Algorithm Implementation on FPGAs”, Semantics, Knowledge and Grid, 2009. SKG 2009. Fifth International Conference, Page(s): 298 – 301. B. Smith, “An approach to graphs of linear forms (Unpublished work style),” unpublished. VIII. CONCLUSIONS [11] Biham, Eli and Shamir, Adi,” Differential Cryptanalysis of the Data This uses Verilog description language to get the modules of Encryption Standard”, Springer Verlag, 1993. ISBN 0-387-97930-1, ISBN 3-540-97930-1. XTEA. After studying the comparative analysis with [3] we conclude that there is a difference in between the number of slices, LUTs, GCLKs and the maximum frequency. While AUTHORS synthesizing our optimization goal is speed. The results are quiet stable and reliable and has great flexibility with high integration. First Author – Shweta Gaba, Pursuing M.Tech in VLSI, Amity School of Engineering and Technology, Amity University and e- mail – [email protected].

REFERENCES Second Author – Iti Aggarwal, Pursuing M.Tech in VLSI, th [1] Extended TEA Algorithm proposed by Tom St Denis, April 20 1999. Amity School of Engineering and Technology, Amity University [2] Julio C. Hernandez, Pedro Isasi “New results on the Genetic Cryptanalysis of TEA Reduced Round versions of XTEA” 2000 IEEE. and e-mail – [email protected] [3] Steven M. Aumack, Michael D. Koontz Jr. “Hardware Implementation of XTEA”. Third Author – Dr. Sujata Pandey, HOI of Electronics and [4] Derek Williams CPSC 6128- Network Security Columbus State University Communication Dept. Amity School of Engineering and “The Tiny Encryption Algorithm (TEA)” April 26, 2008. [5] Gaidaa Saeed Mahdi, “A Modification of TEA Block Cipher Algorithm for Technology, Amity University and e-mail – [email protected]. Data Security (MTEA)”, Eng. & Tech., Journal, vol.29, No.5, 2011. [6] Wheeler, David J. and Needham, Roger M. TEA, “a Tiny Encryption Algorithm” Computer Laboratory, Cambridge University, England. November, 1994.